{ lib, config, pkgs, ... }:
let
  cfg = config.hardware.raspberry-pi;
  render-raspberrypi-config =
    let
      render-options = opts:
        lib.strings.concatStringsSep "\n" (render-dt-kvs opts);
      render-dt-param = x: "dtparam=" + x;
      render-dt-kv = k: v:
        if isNull v.value then
          k
        else
          let vstr = toString v.value; in "${k}=${vstr}";
      render-dt-kvs = x:
        lib.attrsets.mapAttrsToList render-dt-kv
          (lib.filterAttrs (k: v: v.enable) x);
      render-dt-overlay = { overlay, args }:
        "dtoverlay=" + overlay + "\n"
        + lib.strings.concatMapStringsSep "\n" render-dt-param args + "\n"
        + "dtoverlay=";
      render-base-dt-params = params:
        lib.strings.concatMapStringsSep "\n" render-dt-param
          (render-dt-kvs params);
      render-dt-overlays = overlays:
        lib.strings.concatMapStringsSep "\n" render-dt-overlay
          (lib.attrsets.mapAttrsToList
            (k: v: {
              overlay = k;
              args = render-dt-kvs v.params;
            })
            (lib.filterAttrs (k: v: v.enable) overlays));
      render-config-section = k:
        { options, base-dt-params, dt-overlays }:
        let
          all-config = lib.concatStringsSep "\n" (lib.filter (x: x != "") [
            (render-options options)
            (render-base-dt-params base-dt-params)
            (render-dt-overlays dt-overlays)
          ]);
        in
        ''
          [${k}]
          ${all-config}
        '';
    in
    conf:
    lib.strings.concatStringsSep "\n"
      (lib.attrsets.mapAttrsToList render-config-section conf);
in
{
  options = {
    hardware.raspberry-pi = {
      config =
        let
          rpi-config-param = {
            options = {
              enable = lib.mkEnableOption "attr";
              value =
                lib.mkOption { type = with lib.types; oneOf [ int str bool ]; };
            };
          };
          dt-param = {
            options = {
              enable = lib.mkEnableOption "attr";
              value = lib.mkOption {
                type = with lib.types; nullOr (oneOf [ int str bool ]);
                default = null;
              };
            };
          };
          dt-overlay = {
            options = {
              enable = lib.mkEnableOption "overlay";
              params = lib.mkOption {
                type = with lib.types; attrsOf (submodule dt-param);
              };
            };
          };
          raspberry-pi-config-options = {
            options = {
              options = lib.mkOption {
                type = with lib.types; attrsOf (submodule rpi-config-param);
                default = { };
                example = {
                  enable_gic = {
                    enable = true;
                    value = true;
                  };
                  arm_boost = {
                    enable = true;
                    value = true;
                  };
                };
              };
              base-dt-params = lib.mkOption {
                type = with lib.types; attrsOf (submodule rpi-config-param);
                default = { };
                example = {
                  i2c = {
                    enable = true;
                    value = "on";
                  };
                  audio = {
                    enable = true;
                    value = "on";
                  };
                };
                description = "parameters to pass to the base dtb";
              };
              dt-overlays = lib.mkOption {
                type = with lib.types; attrsOf (submodule dt-overlay);
                default = { };
                example = { vc4-kms-v3d = { cma-256 = { enable = true; }; }; };
                description = "dtb overlays to apply";
              };
            };
          };
        in
        lib.mkOption {
          type = with lib.types; attrsOf (submodule raspberry-pi-config-options);
        };

      config-generated = lib.mkOption {
        type = lib.types.str;
        description = "the config text generated by raspberrypi.hardware.config";
        readOnly = true;
      };

      config-output = lib.mkOption {
        type = lib.types.package;
        default = pkgs.writeTextFile {
          name = "config.txt";
          text = ''
            # This is a generated file. Do not edit!
            ${cfg.config-generated}
          '';
        };
      };
    };
  };
  config = {
    hardware.raspberry-pi.config-generated = render-raspberrypi-config cfg.config;
  };
}